The present disclosure generally relates to reagants and membrane-based diagnostic tests.
Microfluidic devices, also known as microPADs or μPADS, offer a promising platform for low-cost, easy-to-use, point-of-care diagnostic assays. In many cases, microPADs are small, portable, may function without supporting equipment like pumps, and may require only small volumes of sample and small amounts (˜1 μg) of reagents. MicroPADs may be inexpensively made from paper or some other porous membrane or material. Conventional application of reagents onto the devices during fabrication is done via solution-based deposition.
Solution-based deposition of reagents onto microPADs usually involves three basic steps: (i) dissolving the reagent in a liquid solvent to prepare a reagent solution; (ii) adding a small volume of the reagent solution to the device in the desired location; and (iii) drying the device to remove the solvent. Solution-based reagent deposition also is commonly used in the fabrication of a variety of membrane- and plastic-based diagnostic devices, and an entire industry of liquid-dispensing technology has grown around the need for applying small volumes of solutions in specific locations onto porous membranes and other substrates.
One common concern with solution-based deposition is that some reagents do not respond well to the drying process. Enzymes, for example, are important reagents for a variety of point-of-care assays and are known to denature when dried from aqueous solution under ambient conditions. A second common concern with solution-based deposition is that some reagents exhibit relatively short “shelf life” after drying. A third concern with solution-based deposition is that some reagents, including antibodies, bind to porous membranes irreversibly when dried from solution, and for certain types of assays it is desirable for the reagent to still be mobile on the device.
Accordingly, an alternative to solution-based deposition that addresses one or more of these concerns is desired.